1. Field of the Invention
The present invention relates to a projection measuring instrument. More specifically, it relates to a projection measuring instrument for enlarging and projecting an image of a minute workpiece for comparative measurement with a template.
2. Description of Related Art
A conventional example is shown in FIG. 4. In the figure, a condenser lens 52, a projection lens 53, and a screen 54 are disposed in this order in an irradiation direction of a light source 51 respectively at a predetermined interval, which composes an observation optical system.
A table 56 for putting a workpiece 55 thereon and a relative movement unit 57 for movably supporting the table 56 are respectively provided between the condenser lens 52 and the projection lens 53.
The relative movement unit 57 movably supports the table 56 in a light axis direction (Z direction) and in two directions orthogonal therewith (X, Y directions) and rotatably supports the table 56 around an axis parallel to the Z direction. The rotary angle is defined as .theta..
The light irradiated from the light source 51 illuminates the workpiece 55 through the condenser lens 52. The shadow of the workpiece 55 is magnified by the projection lens 53 and the workpiece image 58 is irradiated onto the screen 54. The screen 54 is a transparent glass having a detachable diffusion-processed overlay chart, the overlay chart having a template of the workpiece on a surface thereof
Accordingly, as shown in FIG. 5, the workpiece image 58 and the template 59 of the workpiece 55 are simultaneously displayed onto the screen 54. The observer moves the table 56 while checking the indication on the screen 54 to conduct profile measurement by, for instance, superposing the workpiece image 58 of the workpiece 55 and the template 59.
As shown in FIG. 6, displacement of the table 56 is detected by a displacement sensor 61 and, subsequently, displayed on an external display 62.
The displacement sensor 61 has a linear displacement sensor (such as an optical linear encoder) for detecting displacement of the table 56 in XYZ direction and an angle sensor for detecting rotary angle .theta. of the table 56 (such as a rotary encoder). The displacement detected by respective encoders, i.e., respective displacement of the table 56 in XYZ directions are counted by a XYZ counter 61a and the rotary angle .theta. of the table 56 is counted by a .theta. counter 61b respectively to be displayed to the external display 62.
Accordingly, as shown in FIG. 7, when the overlay chart is changed to a cross-hair reticle 63 and the table 56 is moved for relative movement of the line from one end to the other end of the workpiece image 58, the lo displacements X, Y, Z and .theta. at the time are displayed on the external display 62, thereby measuring a dimension of the workpiece 55 by the X, Y, Z and .theta. value displayed onto the external display 62.
However, in the above conventional example, since the overlay chart has to be exchanged in accordance with a type of the workpiece 55 and magnification of the projection lens for comparative observation of the workpiece image 58 and the template 59, exchange work is troublesome.
Further, since the table 56 has to be set at the most appropriate position while looking into the screen 54, the measurement value displayed on the external display 52 was difficult to be checked.